1. Field of the Invention
The present invention relates generally to key operated safety switches. More specifically, the present invention relates to key operated operating heads which are fastened to switch mechanisms to prevent the undesired flow of electricity to dangerous apparatus.
2. Description of the Related Art
The need for safety type switches is increasing throughout the world, particularly in the machine tool industry. Typically, in years past, traditional, simple, limit switches, such as Honeywell model no. LSAlA, were used to sense the position of guards or doors on machining centers. However, machine operators have found simple means of disabling these switches, effectively bypassing them, which allowed the operators easier access to the work area or an increase in their rate of part production. But, the safety features were then neutralized.
International standards have been written to keep the use of traditional limit switches to a minimum, and require Safety Interlock Switching, similar to Honeywell's GK, GKL and GKR series of Key Operated Sensors. Reference may be had to U.S. Pat. No. 5,473,127, to Falcon, et al., of common ownership herewith. There are testing agencies throughout the world which perform tests and authorize Third Party Approval for such products. One of them is BIA, based in Cologne, Germany, that mandates the specifications and requirements for these types of devices. Their specification (GS-ET-19), which covers solenoid locking/unlocking Interlock switches, is very similar to IEC 947-5-1, but with added requirements regarding the bypassing, or defeating, of an Interlock Switch by means of a tool other that the one intended for use. This paragraph, Paragraph 3.23, Protection Against Easy Bypassing is defined to prevent "easy bypassing means operating the lock mechanically by hand or with a simple device such as a tool, pencil, pin, screw, nail, etc. . . . Devices deemed not to be simple are those made using tools in more than one stage".
Thus there is a desire for key operated safety switches which meet this requirement of not being easily defeated by simple tools. Such a device is also desirably made of fewer and more cost effective parts to lessen the economic burden on the purchaser.